Hybrid Energy Storage Systems (HESSs), combining multiple storage technologies such as lithium-ion batteries (LIB) with supercapacitors, hydrogen, flywheels, thermal energy, pumped hydro, and vanadium redox flow batteries, offer comprehensive solutions that enhance grid. Hybrid Energy Storage Systems (HESSs), combining multiple storage technologies such as lithium-ion batteries (LIB) with supercapacitors, hydrogen, flywheels, thermal energy, pumped hydro, and vanadium redox flow batteries, offer comprehensive solutions that enhance grid. Energy storage allows for the capture of energy to be used at a later time, a capability that is important for integrating intermittent renewable energy sources. A hybrid energy storage system (HESS) refines this by combining different storage technologies into an optimized solution. As renewable energy sources like wind and solar continue to grow, integrating an effective storage system has become. The Iowa Stored Energy Park, projected to begin commercial operation in 2015, will use wind farms in Iowa as an energy source in conjunction with CAES. Combining solar and geothermal is also possible.